1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a magnetic film having perpendicular magnetization, the magnetic film being used for a recording layer. The present invention also relates to a recording and reproducing head and a magnetic recording and reproducing method for such a magnetic recording medium. In particular, the present invention relates to a magnetic recording medium on which any disappearance of data, which would be otherwise caused by the thermomagnetic relaxation phenomenon, is prevented or suppressed, and recording and reproduction can be performed at a surface recording density of not less than 20 Gbits/in2. The present invention also relates to a recording and reproducing head and a novel magnetic recording and reproducing method which are preferably used to perform recording and reproduction on such a magnetic recording medium.
2. Description of the Related Art
The hard disk (magnetic recording medium) is widely used as an external storage medium for computers and the like. Usually, the longitudinal magnetic recording is adopted for the hard disk, in which information is recorded in parallel to a recording film surface by using, for example, a ring-shaped magnetic head (hereinafter referred to as xe2x80x9cring headxe2x80x9d) carried on a floating type slider.
In recent years, a variety of data including, for example, graphic data, animation data, and document data are processed in various ways in advanced manners, in which a huge amount of information is dealt with. In order to successfully deal with such a huge amount of data, one of the most important technical tasks in the field of hard disk is to increase the surface recording density. At present, the hard disk has achieved a surface recording density of 4 Gbits/in2.
A means for achieving the high density process has been suggested, for example, in IEEE Transactions on Magnetics, Vol. MAG-15, No. 6, pp. 1456-1458 (1979). This document describes a perpendicular magnetic recording system and a perpendicular magnetic recording medium which are based on the use of a recording film of a Coxe2x80x94Cr film having perpendicular magnetization so that information is recorded in the perpendicular direction with respect to a recording film surface.
In order to further increase the surface recording density of the hard disk, it is known that the magnet (magnetic particle), which is a recording unit for constructing the recording layer, is allowed to have a small size. However, if the magnetic particles are allowed to have a minute size so that the surface recording density is increased to be not less than 10 to 20 Gbits/in2, the following problem arises. That is, the magnetic particles become unstable due to the thermomagnetic relaxation phenomenon, and the recorded data disappears.
The present invention has been made in order to solve the problem involved in the conventional technique as described above, an object of which is to provide a magnetic recording medium in which minute magnetic particles successfully exist in a stable manner, and information subjected to fine recording can be reproduced at a high S/N ratio, even when the surface recording density is increased by using the minute magnetic particles to serve as the recording unit.
Another object of the present invention is to provide a recording and reproducing head which is preferably used to record and reproduce information by using the magnetic recording medium as described above.
Still another object of the present invention is to provided a novel magnetic recording and reproducing method in which information is recorded at a super high density by using the magnetic recording medium and the recording and reproducing head as described above, and the recorded information can be reproduced at a high SIN ratio.
According to a first aspect of the present invention, there is provided a magnetic recording medium comprising:
a substrate;
a recording holding layer composed of a magnetic material; and
a recording layer composed of a ferri-magnetic material having perpendicular magnetization, wherein:
information is recorded by applying a recording magnetic field while heating a predetermined area of the magnetic recording medium so that a recording magnetic domain in the recording layer is inverted, and the information is reproduced by detecting a magnetic field obtained from the recording magnetic domain in the recording layer.
The magnetic recording medium of the present invention includes the recording layer which is formed of the ferri-magnetic material having the perpendicular magnetization, and the recording holding layer which is formed of the magnetic material. The recording holding layer can be composed of, for example, a ferri-magnetic material and an antiferromagnetic material. The recording holding layer is preferably provided between the substrate and the recording layer. Especially, it is preferable that the recording holding layer is provided so that it makes contact with the recording layer with each other. When the recording holding layer is provided as described above, the recording holding layer makes exchange coupling with the recording magnetic domain of the recording layer to hold the recording magnetic domain in a stable state in the perpendicular direction. Those preferably usable as the ferri-magnetic material for the recording holding layer include, for example, rare earth-transition metal alloys such as TbFeCo, GdTbFeCo, TbFeCoCr, TbFe, GdFeCo, GdTbFe, and DyTbFe. Those preferably usable as the antiferromagnetic material for the recording holding layer include, for example, transition metal (Cr, Mn, Fe, Co, Ni) alloys, alloys of noble metal (Au, Pt, Rh, Pd) and transition metal (Cr, Mn, Fe, Co, Ni), and transition metal oxides. For example, it is preferable to use FeMn, NiO, NiMn, PtMn, FeNiMn, AuMn, ZnZr, and FeRh.
Concerning the magnetic recording medium of the present invention, in order to ensure the thermal stability of the recording magnetic domain in the recording layer, it is necessary that the recording layer has a coercive force of not less than 5 kOe within a temperature range from the room temperature (about 10xc2x0 C.) which is the preservation temperature for the medium, approximately to the temperature in the apparatus (about 100xc2x0 C.). Therefore, it is preferable that the recording layer has a coercive force of not less than 5 kOe in a temperature range of 10xc2x0 C. to 150xc2x0 C. However, there is no limitation thereto when a reproducing layer is used to increase the magnetic field from the recording layer as described later on. Further, when the information recorded in the recording layer is reproduced, the magnetic field, which is generated from the recording magnetic domain of the recording layer, is detected. Accordingly, it is advantageous to use a recording layer having a high Curie temperature. Therefore, in order to obtain a sufficient magnetic field intensity from the recording magnetic domain at a temperature in the vicinity of the reproducing temperature, it is preferable that the recording layer has a Curie temperature of not less than 300xc2x0 C.
As described above, when the recording layer having the large coercive force within the temperature range of 10xc2x0 C. to 150xc2x0 C. is used, even if the minute recording mark is formed in the recording layer, then the disappearance of the recording mark is suppressed, which would be otherwise caused by the thermomagnetic relaxation phenomenon after the recording. During the recording, the coercive force of the recording layer can be decreased by heating the magnetic recording medium to a temperature of not less than 200xc2x0 C. Therefore, the recording can be performed with ease by using a weak applied magnetic field. When the recorded information is reproduced, the magnetic field from the recording magnetic domain in the recording layer is directly detected by using, for example, a magnetic resistance element to reproduce the information. In other words, the magnetic recording medium of the present invention is different from the magneto-optical recording medium on which the magnetization state is detected by utilizing the magneto-optical effect (for example, Kerr effect).
The magnetic recording medium of the present invention may further comprise a reproducing layer on the recording layer. It is preferable that the reproducing layer has saturation magnetization which is larger than saturation magnetization of the recording layer at a temperature of not less than the room temperature, preferably in a temperature range of 20xc2x0 C. to 150xc2x0 C. That is, the reproducing layer is capable of generating leak magnetic field which is larger than that of the recording layer. Therefore, when the magnetization of the recording layer is transferred to the reproducing layer to detect the magnetization state of the reproducing layer, it is possible to obtain an amplified reproduced signal. The reproducing layer may be either an in-plane magnetizable film or a perpendicularly magnetizable film.
The magnetic recording medium of the present invention may further comprise a recording auxiliary layer which exhibits soft magnetization. Those usable as a material for constructing such a recording auxiliary layer include, for example, permalloy (NiFe), Fexe2x80x94(Al, Si) alloys, NiFexe2x80x94(Mo, Cr, Cu, Mn, Rh), Co amorphous alloys. The recording auxiliary layer is preferably formed such that the magnetic field is applied thereto via the recording layer. In other words, when the magnetic field is applied from the side of the substrate, it is possible to provide a structure comprising the substrate, the recording layer, and the recording auxiliary layer in this order. When the magnetic field is applied from the side opposite to the substrate, it is possible to provide a structure comprising the substrate, the recording auxiliary layer, and the recording layer in this order. When the recording layer and the recording auxiliary layer are stacked in the order as described above, it is also preferable that an arbitrary layer is allowed to intervene between these layers.
In the present invention, it is possible to provide an arbitrary layer in addition to the recording auxiliary layer and the recording holding layer described above. For example, if the recording layer and the recording holding layer make exchange coupling with each other during the recording, it is difficult to perform the recording corresponding to the recording data. Therefore, it is preferable to provide a recording control layer for breaking the exchange coupling between the both layers at a temperature at which the predetermined area of the medium is heated during the recording (the temperature will be hereinafter referred to as xe2x80x9crecording temperaturexe2x80x9d which is in the vicinity of the Curie temperature of the recording layer in the embodiments as described later on). In order to break the exchange coupling at the recording temperature, it is preferable that the Curie temperature of the recording control layer is set to be not more than the Curie temperature of the recording layer. It is also possible that a lubricating layer, which is composed of, for example, Fombline (product name) or silicon, is formed on the surface of the magnetic recording medium. The provision of the lubricating layer makes it possible to allow the recording and reproducing head to smoothly slide on the medium surface, even when the recording and reproducing head contacts with the magnetic recording medium during the recording and reproduction. Therefore, it is possible to mitigate and reduce the friction between the medium and the head.
The magnetic recording medium of the present invention may further include a texture which is provided on the surface of the substrate. The provision of the texture on the surface of the substrate makes it possible to constantly control the floating amount of the floating type head when the floating type head is allowed to float over the medium.
According to a second aspect of the present invention, there is provided a recording method for recording information on a magnetic recording medium having a recording layer on a substrate, the method comprising the step of:
recording the information by applying a magnetic field in which at least one of intensity and polarity is modulated depending on the information to be recorded by using a magnetic head, while applying heat to a predetermined area of the magnetic recording medium, wherein:
the recording layer is composed of a ferri-magnetic material having perpendicular magnetization; and
a magnetic pole of the magnetic head has a width of not more than 1 xcexcm in a direction perpendicular to a recording direction.
In the recording method of the present invention, it is possible to use, for example, a laser beam in order to heat the predetermined area on the magnetic recording medium. The heating can be effected by collecting and radiating the laser beam onto the predetermined area on the medium by using an objective lens. Accordingly, the coercive force of the recording layer is decreased at only the predetermined high temperature area on which the laser beam is collected. The magnetization is inverted only in the concerning range of the area. Thus, it is possible to form a minute recording magnetic domain. In order to introduce the laser beam into the objective lens, it is preferable to use an optical fiber. The optical fiber successfully introduces the laser beam from a laser light source into the objective lens with good energy efficiency. Another method is available to heat the predetermined area on the magnetic recording medium, in which a heater such as a coil type heater is used. The area, which is located at a position of not more than 1 xcexcm from the surface of the magnetic recording medium, can be heated by using the radiant heat from the heater.
In the recording method of the present invention, for example, it is possible that a plurality of recording magnetic heads are used to simultaneously record a series of divided pieces of information at a plurality of positions on the magnetic recording medium respectively. Accordingly, it is possible to improve the information transfer speed.
According to a third aspect of the present invention, there is provided a reproducing method for reproducing information recorded on a magnetic recording medium having a recording layer, wherein:
the recording layer is composed of a ferri-magnetic material having perpendicular magnetization; and
a magnetic element, which is selected from the group consisting of a magnetic resistance element, a magnetic element having a spin-valve film, and an induction type magnetic element, is used to reproduce the information recorded in the recording layer.
In the reproducing method of the present invention, the recorded information is reproduced by using, for example, the magnetic resistance element, the magnetic element including the spin-valve film, or the induction type magnetic element (induction type magnetic head), while applying the heat to the predetermined area of the magnetic recording medium. The magnetic recording medium may be also heated during the reproduction of information. The magnetic recording medium can be heated, for example, by radiating a laser beam or by applying the radiant heat obtained by using a heater or the like. When the information is recorded, the recording can be performed by applying a magnetic field in which at least one of intensity and polarity is modulated depending on the recording information, while applying heat to the predetermined area of the magnetic recording medium. Further, a series of divided pieces of information, which are recorded at a plurality of positions on the magnetic recording medium respectively, can be simultaneously reproduced by using, for example, a plurality of magnetic heads which carry any one of the magnetic elements described above.
According to a fourth aspect of the present invention, there is provided a recording method for recording information on an information-recording medium including, on a substrate, a recording layer having perpendicular magnetization, the method comprising the step of:
recording the information by irradiating the information-recording medium with a light spot while applying a magnetic field to only an area which is located at the inside of the light spot and which is smaller than the light spot.
In the recording method of the present invention, a recording mark, which is smaller than the light spot, is formed in the area at the inside of the light spot by applying the magnetic field by using, for example, a single magnetic pole head capable of performing perpendicular magnetization recording, while irradiating the information-recording medium with the light spot. Accordingly, it is possible to achieve the super high density recording. In order to form the recording mark which is smaller than the light spot, it is preferable that the single magnetic pole head is machined by means of, for example, FIB (focused ion beam) so that the tip of the single magnetic pole head for generating the line of magnetic force is smaller than the light spot diameter.
According to a fifth aspect of the present invention, there is provided a recording and/or reproducing head for a magnetic recording medium, comprising:
a magnetic field-generating source for applying a recording magnetic field to the magnetic recording medium;
a magnetic element for reading magnetization information on the magnetic recording medium, the magnetic element being selected from the group consisting of a magnetic resistance element, a magnetic element including a spin-valve film, and an induction type magnetic element; and
an air slider which carries the magnetic field-generating source and the magnetic element.
The head of the present invention may further comprise a heat source for heating the magnetic recording medium. For example, a laser light source can be used as the heat source. A predetermined area of the medium can be heated by collecting and radiating the laser beam radiated from the laser light source by using an objective lens or the like. In order to introduce the laser beam into the objective lens, for example, it is possible to use an optical fiber. It is desirable that the heat source is provided so that it is arranged at a frontward position (leading side) with respect to the magnetic element in a direction of movement of the magnetic recording medium. In this document, the frontward position (leading side) of an object in a direction of movement of the magnetic recording medium means one side of first and second sides between which the object is positioned and on which the magnetic recording medium approaches first, when the magnetic recording medium is moving toward the object. The backward position (trailing side) of an object in a direction of movement of the magnetic recording medium means one side of first and second sides between which the object is positioned and on which the magnetic recording medium approaches second or later, when the magnetic recording medium is moving toward the object.
The magnetic field-generating source for applying the recording magnetic field to the magnetic recording medium, which is included in the head of the present invention, is constructed, for example, by using a single magnetic pole head 220 as shown in FIG. 20. The single magnetic pole head 220 principally comprises a core (main magnetic pole) 225, a main body 221, and a coil 224 wound around a connecting section 223 therebetween. A protective film may be formed on the inner wall of the core 225. The core 225 is preferably machined by means of, for example, FIB (focused ion beam) so that the width of the tip of the core is not more than 1 xcexcm in the widthwise direction of the track of the magnetic recording medium when the core 225 is opposed to the magnetic recording medium having a plurality of tracks. Accordingly, the information can be recorded at a super high density on the magnetic recording medium. Further, a part of the single magnetic pole head for generating the magnetic field or the entire single magnetic pole head may be constructed by using, for example, a material such as CoNiFe or CoNiFe alloy in which the saturation magnetic flux density (Bs) is not less than 2.0 T. By doing so, it is possible to increase the magnetic force generated by the single magnetic pole head, and it is possible to record the information on the recording medium having a high coercive force.
In the head of the present invention, the magnetic resistance element is an element (MR device: Magneto-Resistive Device) in which the electric resistance varies depending on the change of the magnetic field. Accordingly, the magnetic resistance element makes it possible to detect the magnetization state of the recording layer in the perpendicular direction and the magnetization state of the other magnetic layers in the perpendicular direction and in the in-plane direction. The material for the MR device may be, for example, FeMn/CoNi/Cu/Co. Further, it is possible to use the magnetic element including the spin-valve film and the magnetic element such as the induction type magnetic head. The spin-valve film may be formed, for example, by using CoFe/Cu/CoFe/Ru/CoFe/MnPt. Alternatively, a GMR (Giant Magneto-Resistive) device, which has a large ratio of the change of electric resistance with respect to the change of magnetic field as compared with the MR device, may be also used in place of the magnetic resistance element.
In the present invention, it is desirable that the air slider is constructed by using a plurality of materials having different coefficients of thermal conductivity. Especially, it is desirable that a material having the lowest coefficient of thermal conductivity, of the plurality of materials having the different coefficients of thermal conductivity is provided between the magnetic field-generating source and the magnetic resistance element. Accordingly, the magnetic resistance element is prevented from being heated by the heat generated by the magnetic field-generating source. Further, a material having the highest coefficient of thermal conductivity, of the plurality of materials having the different coefficients of thermal conductivity is formed at a portion, for example, on the upper surface of the head which contacts with the ambient air. By doing so, the heat, which is generated by the magnetic field-generating source, can be released to the outside of the head.